There is much interest in developing electrophoretic deposition systems that can be used to provide flaw-free coatings for electrical components and high performance applications. Aqueous electrodepositions have been known for at least fifty years, but are limited to resins possessing suitable functionality to convert them to water dispersible systems suitable for electrodeposition. Typical polymers include epoxy resins, acrylics, carboxylic acid polymers, and vinyl acetate-maleic acid copolymers. These materials are rendered water dispersible by reaction with amines to form their respective salts. Recent studies have led to the development of electrodeposition systems of high performance polymers in non-aqueous media. Even in these systems the presence of amine was a necessary component in order to prepare suitable electrophorettable emulsions.
One class of polymers that has been converted to an electrophorettable system is the polysulfones. Complete details of the preparation of these polymers and their conversion to electrophoretic emulsions can be found in U.S. Pat. No. 4,003,812.
The use of polysulfone polymers as electrodeposition systems offers many advantages compared to carboxyl-containing resins. Some of these advantages include elimination of the very high temperatures such as those required for polyimides (300.degree. to 350.degree. C.), the fact that the polysulfones do not produce condensation products as do polyimides, their lower cost, their good electrical properties, and the elimination of the copper chelation that occurs with carboxyl containing polymers, which has a deleterious effect on coating properties.
While the system described in U.S. Pat. No. 4,003,812 produces satisfactory polysulfone coatings, research has continued on ways of improving the system by eliminating components or processing steps, or producing coatings with better properties.